Over the past several years, the demand from businesses and individuals alike for second day and even overnight deliveries of articles, such as small to mid-sized parcels, packages and letters, has steadily increased. This demand is due, in part, to the prevalence of Internet and mail order shopping, which creates a similar need for an efficient and effective distribution system to deliver expediently the wares to a common carrier. Consequently, the need for methods and systems for quickly transporting, sorting and distributing this ever increasing volume of articles has similarly increased.
In fact, it is now general practice for common carriers to transport articles in the form of small to mid-sized packages or the like to a central sorting terminal or hub, where they are sorted according to selected parameters, such as having common regional destinations, and then delivered as a group. Once these destinations are reached, it is necessary to sort again to distribute articles in the group to their final destinations. To accomplish these tasks in the amount of time required to insure overnight delivery, the central as well as the regional sorting terminals or hubs must receive, sort and distribute hundreds of thousands of coded packages each day. Besides on the delivery side, a similar need exists on the distribution side, since purchasers are accustomed to receiving ordered items without significant delay.
Necessarily, the sortation systems used must be capable of processing the packages within these defined time parameters. Indeed, in response to the continuously increasing number of packages requiring next day or overnight delivery, the sortation systems must operate much faster and more efficiently than just a few years ago. It is also desirable for the systems to be more adaptable to accommodate fluctuations in need/demand, as well as simpler and less expensive.
Since as early as the 1960's, various package sortation systems have relied upon primitive “induction” type systems including an endless “loop” conveyor with mobile units that receive, transport and deposit packages at selected distribution stations. Specifically, U.S. Pat. No. 3,167,192 to Harrison et al. and U.S. Pat. No. 3,327,836 to Burt each disclose package sortation systems using tilt tray assembly units propelled by an endless conveyor chain. Timers and somewhat unreliable magnetic readers actuate tip solenoids to tilt the trays to one side, thus in theory allowing gravity to pull passively the packages from atop the trays upon reaching their destination. As should be appreciated, the speed with which such a system can process articles leaves much to be desired, especially since articles must potentially traverse the entire loop before reaching the desired destination.
A more recent sortation system described in U.S. Pat. No. 4,832,204 to Handy et al. integrates these prior art tilt tray sortation systems with more complicated scanning equipment and computer control in an attempt to improve overall system speed and efficiency. Despite the successful integration of these components into a supposedly more modern and state of the art system, but with much greater complexity and cost, the system of the '204 patent still fails to improve the basic sortation apparatus and methods. In essence, package delivery customers are calling for a move away from the continued reliance on the complex and expensive tilt tray systems that rely primarily on gravity transfer, such as in the '204 patent, and at the same time demanding significant increases in the overall speed, efficiency and adaptability of the sortation system.
In recent times, “tilt tray” sorters have been replaced by allegedly more efficient “cross belt” sorters. One version of this type of sortation system includes an endless train of driven cars pass operator-controlled feed conveyors used to deliver a single article for transport around the loop. When the car reaches the desired destination for the article, an onboard conveyor actuates to eject the article to a takeaway conveyor. An early example of this type of system appears in U.S. Pat. No. 3,977,513 to Rushforth, and a more modern example appears in the September 2003 issue of Modern Material Handling magazine (incorporated herein by reference).
Despite the industry-wide movement toward this type of sorting system, it still suffers from similar problems with efficiency. Just like in the tilt tray systems, only a single article can be loaded onto a selected car at a given instant in time. This serves as a significant limitation on the total throughput possible, and requires operating many such systems simultaneously to keep up with the demand. The use of individual cars with cross belts, which are typically complicated, also presents problems from a reliability and maintenance standpoint.
Furthermore, past sortation systems cannot sort articles continuously, since various events demand downtime. For example, articles sometimes mis-introduced into the system must be retrieved and removed. Likewise, completing the previous sorting operation before introducing the next group of articles requires introducing any articles accidentally left out from the previous operation, which results in costly downtime. Running two induction-type sortation systems in parallel alleviates the problem in part, but this will not necessarily reduce the cost. The existing systems also tend to occupy a great deal of floor space, which may make this impossible to accomplish using a given facility.
Thus, an important aspect of the effort to improve this technology involves providing a sortation system and related method capable of transporting, sorting and distributing the increasing volume of such articles in a more efficient manner. Increased efficiency and adaptability of use, as well as lower cost and maintenance, should advantageously result without a concomitant increase in complexity.